Refrigerating device with cooling unit working intermittently

ABSTRACT

In a refrigerating device consisting of a housing unit 1 and a cooling unit 2 the cooling unit 2 includes an evaporator 3, a condenser 4 and a reactor 5. The evaportor 3, the condenser 4 and the reactor 5 form a first closed system 27 in which ammonia is provided for as working liquid and manganese chloride 5 is provided for in the sorber part 6 of the reactor 5. The reactor 5 has an insulating shell 16 enclosing the sorber part 6, wherein a working chamber 17 filled with working liquid 18 is reserved between the insulating shell 16 and the sorber part 6. To the working chamber 17 a second closed system 19 is connected in the upper and lower region of the working chamber 17. The upper connection can be closed by means of a shut-off valve 24. By heating the working liquid and thus the sorber part 6 in the regeneration phase by means of a heating means 25 and by cooling the sorber part by means of the working liquid 18 during the sorption phase the efficiency of the refrigerating device is increased substantially.

The invention relates to a refrigerating device including a housing unitand a cooling unit working intermittently, the cooling unit comprisingan evaporator accommodated in the housing unit, a condenser and areactor with a heatable sorber part filled with a substance capable ofsorbing a working liquid at standard temperature and again releasing itupon heating, and wherein the evaporator, the condenser and the sorberpart are mutually connected by a line and form a closed system.

Refrigerating units of the above kind are in particular used insmall-size refrigerating devices and air coolers of air conditioningsystems. In the sorber part the substance capable of sorption andenriched with a working liquid is heated and therein releases theabsorbed liquid in form of vapor. The vapor condenses in the condenserand the condensed liquid collects in the evaporator arranged in thehousing unit of the refrigerating device. When the heat source for thesubstance capable of sorption is switched off and the substance coolsdown, the material sucks in the moisture from the line saturated withvapor and therein creates low pressure in the line, which makesevaporate the liquid contained in the evaporator and, if applicable,makes it boil at low temperature. The evaporator therein withdraws heatfrom the environment in the housing unit and, therefore, can be used ascooling part. Such refrigerating devices are of simple construction anddo not include movable parts. As substance capable of sorption e.g. azeolite reacting with water in the above-described manner can be used.The water therein due to the low pressure will boil at few degrees and,if applicable, also in case of minus degrees in the evaporator. Forrefrigerating devices of this kind, however, also other sorptionsubstances and liquids are suited, like e.g. salt and ammonia.

When expelling the liquid from the substance capable of sorption it isimportant that the substance is heated as uniformly as possible. Thiscreates difficulties in particular then when heating is effected using aheat source--as is the case in refrigerating units--which is to beindependent from the kind of heating (electric current, gas, dry fueland the like). As the temperature of a flame is very high as compared tothe amount of heat produced, it is important in a sorber part of thekind in discussion to transfer the heat to the substance capable ofsorption such that local overheating is avoided. A further demand liesin that overheating of the sorber part should be avoided in thedesorption phase because then the sorption activity of the sorber partwill slowly calm down and thus cooling in the housing wall of therefrigerating device is reduced.

The invention, therefore, is based on the object of arranging anddesigning the reactor accommodating the sorber part in a refrigeratingdevice of the generic kind such that the efficiency of the sorption andregeneration phases of the cooling unit is improved and safe functioningof the intermittent operation is guaranteed in spite of a simpleconstruction and the use of different heating sources.

In accordance with this present invention, the reactor of the coolingunit is equipped with a second closed system filled with a workingliquid, which system in the sorption phase of the refrigerating unit iscontrollable as cooling system for the sorber part and in theregeneration phase of the refrigerating unit--as heating system for thesorber part. Thus, two closed systems are provided for which inadvantageous manner are connected in parallel to one another and areevacuated prior to being filled with working liquid. The first systemessentially consists of the evaporator arranged in an insulation in theupper part of the housing unit of the refrigerating device andcomprising a container for receiving the working liquid as well as apipe protruding from the container in downward direction into the spaceto be cooled and an evaporator pipe connected subsequently thereto andreaching until above the level of working liquid in the container.Furthermore, the first closed system comprises a connecting line betweenthe evaporator and the sorber part, said line consisting of severalsections, namely a pipeline essentially extending perpendicularly with acomparatively small cross-sectional area, which is followed by asnake-shaped ascending, pipeline having a larger cross-sectional areaand which again engages with the sorber part by means of a descendingpipeline, the end of said descending line having corresponding openingsthrough which the evaporated working liquid can penetrate into thesubstance capable of sorption. As working liquid e.g. ammonia offersitself, which in vapor form enters the substance capable of sorption,e.g. manganese chloride by the strong affinity of which to ammonia issorbed. The reactor itself in advantageous manner can consist of twohousing parts arranged concentrically and with a distance to oneanother, the inner housing part being the sorber part filled withsorption material and the outer housing part being an insulating shellcompletely surrounding the sorber part. The space located between thetwo housing parts is filled with the working liquid of the second closedsystem, the second closed system being connected to the working chamberof the reactor in an upper and a lower region.

The heating means of the sorber part can be arranged in the lowerportion of the working chamber of the reactor and can be washed aroundby the working liquid, namely water. However, according to a furtherembodiment it also is conceivable that the heating means is arranged ina small separate chamber connected to an upper and a lower section ofthe working chamber for forming a heating circulation. Therein, theheating means can advantageously be an electrical heating cartridge andin addition a gas-heated pipe guided along the working chamber can beprovided for in the area of the heating cartridge in particular, thispermitting in advantageous manner that either electrical energy or alsogas or dry fuel, respectively, or the like can be used as heat sourceor, however, for achieving a particularly high heating efficiency bothheating means can be used simultaneously. In this way the refrigeratingdevice in accordance with the present invention becomes independent fromthe kind of energy and thereby it can be used in hotels, campingvehicles or boats.

For safety reasons a separate connecting line can be provided foroutside of the working chamber between the lower connecting line of thesecond closed system and the lower connecting line of the heatingcirculation. This connecting line as safety means can serve forproviding the comparatively small heating chamber of the heatingcartridge with return water from the second closed system for avoidingthat the heating cartridge is not washed with water.

In advantageous manner, the second closed system includes aheat-insulated ascending tube connected to the upper region of theworking chamber of the reactor as well as snake-shaped cooling pipeconnected subsequently thereto, a reservoir and a descending pipeconnecting the latter with the lower region of the working chamber. Ashut-off valve which is opened in the sorption phase and is closed inthe regeneration phase is provided for in the ascending pipe above thesorber part.

According to a further advantageous feature of the invention, thereactor can be disposed in the lower portion of the refrigerating deviceand the reservoir can be located above the sorber part of the reactor.This has the advantage that in the sorption phase in case of openedvalve the working chamber can be completely filled with liquid from thereservoir due to gravity . In another embodiment the reactor can bearranged in the upper portion of the refrigerating device and thereservoir can be located below the sorber part of the reactor, here,however, a pump being provided for in the second closed circulation. Theadvantage of this construction lies in that in case of the pump beingswitched off in the regeneration phase the working liquid can flow backfrom the working chamber into the reservoir by means of gravity. Incontrast thereto, the pump starts working in the sorption phase forpumping liquid from the reservoir into the working chamber, where itwashes around the sorber part and cools it.

Switching of the cooling unit from sorption operation to regenerationoperation or vice versa preferably is effected in dependence on a givenmeasurable variable. This measurable variable may be the temperature ofthe cooling water, e.g., in the second closed system or it maycorrespond to a given heat output of the reactor part during thesorption phase or finally it also is conceivable that the time isdetected in which a given amount of ammonia, maybe the entire amount, isevaporated so that the container 7 is empty and thus the sorptionactivity of the sorber part is finished. Finally, it also is conceivablethat the measurable variable is predetermined by adjusting a thermostatin the cooling chamber of the refrigerating device. It this temperatureis reached, an electrical switching of the valve or switching on,respectively, or off of the heating means can be effected.

Further features, details and advantages of the invention result fromthe subsequent description of preferred embodiments with reference tothe drawings, wherein;

FIG. 1 shows a schematic total view of the refrigerating deviceaccording to the present invention;

FIG. 2 shows a schematic cut view along the line II--II of FIG. 1;

FIGS. 3 to 6 show further preferred embodiments of the reactor part andthe system connected thereto.

The refrigerating device in accordance with the present inventionessentially includes a housing unit 1 and a cooling unit 2. The coolingunit 2 works intermittently, and essentially consists of an evaporator 3arranged in an insulated part of the housing unit, a condenser 4 and areactor 5 with a heatable sorber part 6.

The evaporator 3 comprises a container 7 partly filled with the workingliquid ammonia 8. Starting from the bottom of the container, a coolingpipe 9 extends in downward direction into the space 10 to be cooled, ofthe housing unit 1 and is connected to a cooling plate 11. The coolingpipe 9 is followed by an evaporator pipe 12 reaching into the container7 upwardly above the level of the liquid.

The evaporator 3 is connected to a pipeline 13 essentially extendingvertically which is followed by a serpentine or snake-shaped pipeline 14and a vertical pipe 15. The cross-sectional area of the snake-shapedpipeline 14 and the vertical pipe 15 is greater than that of thepipeline 13. The pipe 15 protrudes into the sorber part 6 of the reactor5 and comprises openings through which the evaporated ammonia canpenetrate into he sorption material.

The reactor 5 essentially consists of two housing parts 6 and 16respectively, the housing part 6 corresponding to the sorber part,whereas the housing part 16 is an insulating shell enclosing the sorberpart on the front face in positive manner and on the shell side with adistance to the sorber part outside surface. In this way a workingchamber 17 completely or partly filled with the working liquid 18 (waterin particular) is defined between the sorber part 6 and the insulatingshell. In the upper and lower sections of the working chamber 17 asecond closed system 19 is connected to the reactor 5. This secondclosed system essentially includes a heat-insulated ascending pipeline20, a snake-shaped cooling pipe 21 connected subsequently thereto, areservoir 22 and a descending pipe 23 connecting the latter with thelower section of the working chamber 17. A shut-off valve 24 thefunction of which will be explained later is disposed in the ascendingpipeline 20.

A heating means 25, in this embodiment being an electrical heatingcartridge, is provided for below the sorber part 6 within the workingchamber 17. As can be seen, the electrical heating cartridge 25 iscompletely washed around by working liquid 18. In case of an openedvalve 24 the liquid level 26 is reached so that the sorber part 6 andthe heating means 25 are washed around with water completely. Thisoperational position characterizes the sorber phase, which will still bediscussed further hereinafter. In the regeneration phase during whichthe heating cartridge 26 is working an operational condition as shown inFIG. 2 can be established in which rising vapor in the upper part of theworking chamber with closed valve 24 creates such a pressure conditionthat the working liquid 18 is pressed through the descending pipe 23 tothe reservoir 22.

As can further be seen from FIG. 1, the reactor 5 is disposed in thelower part of the refrigerating device in lying position. The firstclosed system 27 which is composed of the evaporator 3, the pipelines13, 14, 15 and the sorber part 6, is connected in parallel to the secondclosed system 19. Both systems are evacuated closed systems and arelocated one beside the other on the backside and outside of the housingunit, wherein the heat is emitted to the outside, for example byradiators 28 in common manner to the ambient air.

The following figures are different embodiments, however, correspondingparts are marked with corresponding reference numbers. Nor is the entirerefrigerating device shown, but only the reactor part with the secondclosed system 19.

As can be seen from FIG. 3, the reactor 5 is disposed in verticaldirection in the lower part of the housing and the reservoir 22 islocated above the sorber part 6 so that the sorber part 6 arranged inthe working chamber 17 is completely washed around with working liquid,namely water 18. Also in this embodiment an ascending pipe 20 merginginto the cooling pipe 21, the latter being connected to the reservoir22, is subsequent to the upper part of the working chamber 17. The lowerpart of the working chamber 17 is connected to the reservoir 22 via thedescending pipe 23.

While in case of opened valve--i.e. in the sorption phase--a liquidlevel 26 is provided for in the system and the sorber part 6 thus iscompletely washed around by water, in case of closed valve--i.e. in theregeneration phase--an operational condition will occur in which theliquid level sinks down to the level 29, this will, however, be dealtwith later.

It furthermore can be seen from FIG. 3 that in the lower portion of theworking chamber 17 a separate chamber is provided for in which theelectrical heating means 25 is arranged. A heatable gas pipe 31 which isheated by the gas flame 32 and can be used for heating the workingliquid in the chamber 30 beside the heating means 25 is disposed indirect contact to the shell surface of the chamber 30. In this way onedoes not depend on the energy source.

In the embodiment shown in FIG. 4, is can be seen that the chamber 30now no longer is in direct connection with the working chamber 17 of thereactor 5 but is connected to the upper and lower, respectively, portionof the working chamber 17 through an upper line 33 and a lower line 34.It can further be seen that a connecting line 35 is provided between thedescending pipe 23 and the lower line 34, by which it can be guaranteedthat a liquid level not being too low is prevailing in the chamber 30and thereby possibly overheating of the sorber part 6 might be caused.This connecting line 35 therefore more or less takes over a safetyfunction.

In contrast to the embodiments 3 and 4 in which the reactor 5 isarranged in the lower portion of the refrigerating device and thereservoir 22 is provided for on a higher level, the reactor 5 in theembodiments under FIGS. 5 and 6 is arranged in the upper portion of therefrigerating unit, whereas the reservoir 22 is located below the sorberpart 6. Therein the construction of the reactor 5 under FIG. 5essentially is corresponding to the reactor 5 under FIG. 3, while thereactor 5 under FIG. 6 essentially corresponds to the constructionaccording to reactor 5 under FIG. 4.

It has to be remarked that no shut-off valve is provided for any more inthe connecting line 36 by which the second closed system 9 is connectedto the upper portion of the working chamber 17. For this reason theconnecting line 36 also has a comparatively small cross-sectional areain contrast to the snake-shaped cooling pipe 21. As the level of theliquid 26 due to the particular arrangement of the reservoir 22 islocated below the sorber part 6, the liquid has to be pumped into theworking chamber 17 with the aid of a pump 37 for achieving the liquidlevel 38. In this status of the sorption phase the sorber part 6 can becooled efficiently. In the regeneration phase, however, the pump 37 isswitched off and the liquid flows from the working area through thelines 23, 21 back into the reservoir 22. Also in this case a connectingline 35 is provided for between the lines 23 and the separate chamber 30so that it is guaranteed that always a sufficent amount of water forgenerating vapor is available in the chamber 30, wherein the vaporstreams upwardly and condenses on the sorber part 6 for then againdropping downwardly. In this way an excellent heat transfer from theheating cartridge to the sorber part 6 is achieved and the efficiency ofthe device is increased substantially.

It may, of course, occur that a minor vapor portion also reaches thereservoir through the line 36, this however not causing remarkable heatlosses due to the comparatively small cross-sectional areas of theconnecting line 36 and the arrangement thereof within the insulatingshell of the reactor 5.

The operating mode of the device in accordance with the presentinvention is as follows:

During the sorption phase (cooling phase) the shut-off valve 24 in thedevices under FIGS. 1 to 4 is open, while in the devices under FIGS. 5and 6 the pump 37 is switched on. Due to the strong affinity of themanganese chloride in the sorber part 6 the ammonia 8 evaporates in theevaporator 3 and with comparatively low pressure flows through thepipelines 14, 15 into the sorber part 6, where it is absorbed in themanganese chloride. As the ammonia vapor has a very low temperature of,for example -35°, the slight heating during passage through the lines 14and 15 with low pressure does not cause condensation. In sorption of theammonia vapor in the sorber part 6 heat is generated, while in thecooling chamber 10 cold is created by absorption of the heat inevaporation of ammonia. As the sorber part without suitable cooling canincrease to substantial temperatures and, therefore, the sorptionefficiency decreases rapidly, the water contained in the second closedsystem 19 serves for cooling the sorber part 6. The water which in caseof opened valve 24 is at the liquid level 26, for this purpose washesaround the entire sorber part along the shell surface thereof. Vaporcreated by heat given from the sorber part to the cooling agent waterraises in the ascending pipe 20 upwardly and condenses in the coolingpipe 21 so that it is returend to the reservoir 26 in form of liquid.

If after some time the sorption operation has terminated by that theammonia in the evaporator 3 is evaporated completely or that e.g. aparticular temperature priority adjusted by a thermostat has beenobtained in the cooling chamber 10 or the heating of the sorber partdecreases remarkably and, thus, the cooling water temperature decreases,it is switched from the sorption phase to the regeneration phase, thisbeing effected automatically in dependance on the given measuringvalues. This means e.g. that the valve 24 is closed for the regenerationphase and the heating means 25 is switched on (see FIGS. 1 to 3) and/or,respectively, that the pump 37 is switched off and the heating means 25and/or 32 is switched on (see FIGS. 5, 6).

In the regeneration phase the ammonia again is expelled from the sorberpart and through the lines 15 and 14 returns with comparatively highpressure of, for example 10 to 20 bar and a comparatively hightemperature of 180° to 200° C. through the line 13 in liquid form intothe container 7 of the evaporator, as it condenses in the cooling line14. In the reactor 5 the heating output of the heating cartridge 25causes boiling of the working liquid 18 in the working chamber 17 sothat vapor rises upwardly and the liquid presses through the pipe 23into the reservoir 22, vapor bubbles condensing in the cooling pipe 21and flowing back into the reservoir in form of water. A very efficienttransfer of the heating output of the heating cartridge 25 to the sorberpart 6 is achieved by the creation of vapor in the upper portion of theworking chamber, since the vapor in the sorber part 6 in the upperportion with complete and close contact condenses on the cooler surfaceof the sorber region for flowing down as liquid.

In FIG. 4 the vapor pressure causes a lowering of the liquid up to thelevel 29, i.e. up to below the sorber part 6 so that an excellent heattransfer to the sorber part 6 can be effected by means of the vapor.Apart therfrom this construction under FIG. 4 has the advantage thatonly a very small portion of water has to be heated in the comparativelysmall chamber 30 so that this device reacts comparatively quickly.

As soon as the entire ammonia is expelled from the sorber part 6, thedevice automatically changes back to sorption operation. For thispurpose, again regulating values in form of temperature, quantitymeasurement, time measurement and the like can be used which reveal thatthe expelling operation has been terminated.

I claim:
 1. Refrigerating device including a housing unit (1) and acooling unit working intermittently, wherein the cooling unit (2)comprises an evaporator (3) received in the housing unit, a condenser(4), and a reactor (5), said reactor including a heatable sorber part(6) filled with a substance capable of sorption which, at standardtemperature, absorbs a first working liquid and releases said firstworking liquid upon heating, and wherein the evaporator and thecondenser are connected by a first line and the condenser and the sorberpart are connected by a second line and cooperate to form a first closedsystem containing said first working liquid and permittingbi-directional flow of said first working liquid between said evaporatorand said sorber part via said condenser, wherein said reactor (5) isprovided with a second (19) closed system filled with a second workingliquid (18), said second closed system, in the sorption (cooling) phaseof the refrigerating device, serves as a cooling system for the reactor(5) and, in the regeneration phase of the refrigerating device, servesas a heating system for the reactor, and wherein a connection betweensaid condenser and said first line is relatively below a connectionbetween an opposite end of said first line and said evaporator. 2.Refrigerating device as defined in claim 1, wherein said first (27) andsaid second (19) closed systems are connected in parallel with oneanother.
 3. Refrigerating device as defined in claim 1 or 2, whereinsaid first (27) and said second (19) closed systems each include aradiator.
 4. Refrigerating device as defined in claim 1, wherein saidfirst and second closed systems (19, 27), prior to filling with theworking liquids (8, 18), are evacuated.
 5. Refrigerating device asdefined in claim 1, wherein said first working liquid (8) of the firstclosed system (27) is ammonia, the sorption material is a salt, and thesecond working liquid (18) of the second closed system (19) is water. 6.Refrigerating device as defined in claim 1, wherein said evaporator (3)comprises a container (7) disposed in an insulated, upper part of thehousing unit (1) and has a cooling pipe protruding into the space to becooled and being connected to a cooling plate and an evaporator pipe,said evaporator pipe extending into said container and above a level ofworking liquid therein.
 7. Refrigerating device as defined in claim 1,wherein a connecting line between the evaporator and the sorption partof the reactor comprises at least one pipeline (13) with a relativelysmall cross-sectional area and extending essentially horizontally, and asnake-shaped cooling pipe with a relatively enlarged cross sectionalarea extending into the reactor, and having a perforated sectionreceived in the sorption material.
 8. Refrigerating device as defined inclaim 1, wherein said reactor comprises two housing parts arrangedconcentrically and spaced a distance from one another, wherein an innerhousing part is the sorber part (6) filled with sorption material and anouter housing part is an insulating shell (16) completely enclosing thesorber part, the working chamber (17) between the housing parts isfilled with the second working liquid of the second closed system. 9.Refrigerating device as defined in claim 1, wherein said reactor has aworking chamber with upper and lower portions, and said second closedsystem is connected to said upper portion and said lower portion. 10.Refrigerating device as defined in claim 9, wherein said heating meansof the sorber part is disposed in the lower portion of the workingchamber of the reactor and is washed by the second working liquid. 11.Refrigerating device as defined in claim 10, wherein said heating meansis arranged in a separate chamber (30) connected with an upper and alower section of the working chamber to form a circulation path. 12.Refrigerating device as defined in claim 10 or 11, wherein said heatingmeans (25) is an electrical heating cartridge.
 13. Refrigerating deviceas defined in claim 10 or 11, wherein said heating means is formed by anelectrical heating cartridge and a working chamber filled with a workingagent.
 14. Refrigerating device as defined in claim 10 or 11, wherein alower connecting line of the second closed system and of the heatercirculation are connected to one another outside of the working chamberof the reactor.
 15. Refrigerating device including a housing unit (1)and a cooling unit working intermittently, wherein the cooling unit (2)comprises an evaporator (3) received in the housing unit, a condenser(4), and a reactor (5), said reactor including a heatable sorber part(6) filled with a substance capable of sorption which, at standardtemperature, absorbs a first working liquid and releases said firstworking liquid upon heating, and wherein the evaporator, condenser, andsorber part are fluidly connected and cooperate to form a first closedsystem containing said first working liquid, wherein said reactor (5) isprovided with a second (19) closed system filled with a second workingliquid (18), said second closed system, in the sorption (cooling) phaseof the refrigerating device, serves as a cooling system for the reactor(5) and, in the regeneration phase of the refrigerating device, servesas a heating system for the reactor, and wherein said reactor defines aworking chamber surrounding said sorber part, said working chamberhaving an upper portion and a lower portion, said second closed systemcomprises a heat-insulated ascending pipe (20) connected to the upperportion of the working chamber, a cooling pipe (21) connected to anopposite end of said ascending pipe, a reservoir (22), and a descendingpipe (23) connecting the reservoir to the lower portion of the workingchamber.
 16. Refrigerating device as defined in claim 15, wherein ashut-off valve (24) is arranged in said ascending pipe (24). 17.Refrigerating device as defined in claim 16, wherein said shut-off valve(24) is open during the sorption phase and is closed during theregeneration phase.
 18. Refrigerating device as defined in claim 15,wherein said reactor (5) is arranged in a lower portion of therefrigerating device and the reservoir is disposed above the sorber partof the reactor.
 19. Refrigerating device as defined in claim 1, wherein,depending on a given measuring magnitude, the cooling unit switchesbetween the sorption operation and the regeneration operation. 20.Refrigerating device as defined in claim 19, wherein the measuringmagnitude corresponds to a given temperature of the cooling water. 21.Refrigerating device as defined in claim 19, wherein the measuringmagnitude corresponds to a given heat output of the reactor part. 22.Refrigerating device as defined in claim 19, wherein the measuringmagnitude corresponds to a given amount of ammonia in the evaporator.23. Refrigerating device as defined in claim 19, wherein the measuringmagnitude corresponds to a given temperature measurable by an adjustablethermostat in the refrigerating device.
 24. Refrigerating deviceincluding a housing unit (1) and a cooling unit working intermittently,wherein the cooling unit (2) comprises an evaporator (3) received in thehousing unit, a condenser (4), and a reactor (5), said reactor includinga heatable sorber part (6) filled with a substance capable of sorptionwhich, at standard temperature, absorbs a first working liquid andreleases said first working liquid upon heating, and wherein theevaporator, condenser, and sorber part are fluidly connected andcooperate to form a first closed system containing said first workingliquid, wherein said reactor (5) is provided with a second (19) closedsystem comprising a working chamber (17) and a reservoir (22) and beingfilled with a second working liquid (18), said second closed system, inthe sorption phase of the refrigerating device, serves as a coolingsystem for the reactor (5) and, in the regeneration phase of therefrigerating device, serves as a heating system for the reactor, andwherein a pump is provided in the second closed system and the reactor(5) is arranged in the upper part of the refrigerating device and thereservoir (22) is arranged below the sorber part of the reactor forenabling a backflow of a part of the working fluid, from the workingchamber (17) to the reservoir (22) when the pump is switched off.